Diagnosing the fuel pump
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7th Gear
Joined: May 2009
Posts: 7
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From: Dove Canyon, CA
Diagnosing the fuel pump
Before I go to the trouble of dropping the tank or lifting the bed to replace the fuel pump, I want to do diagnose the problem first.
- There’s no pressure on the fuel rail.
- The fuel pump fuse and relay are working properly. 12 volts is leaving the relay.
- I know that a new pump has 0.6 ohms.
- I disconnected the wires to the fuel pump under the car and the fuel pump resistance is 1.6 ohms.
- The four connector pins are a bit corroded.
Now here’s the weird part. When I turn the key on, the voltage coming out of the fuel pump wiring (at the tank) jumps to 12.6 volts but then immediately falls to 6.8 volts. It does that every time. What is going on there?
- There’s no pressure on the fuel rail.
- The fuel pump fuse and relay are working properly. 12 volts is leaving the relay.
- I know that a new pump has 0.6 ohms.
- I disconnected the wires to the fuel pump under the car and the fuel pump resistance is 1.6 ohms.
- The four connector pins are a bit corroded.
Now here’s the weird part. When I turn the key on, the voltage coming out of the fuel pump wiring (at the tank) jumps to 12.6 volts but then immediately falls to 6.8 volts. It does that every time. What is going on there?
Fleet Owner
Joined: Aug 2005
Posts: 23,668
Likes: 301
From: Easton,Ks
The PCM Computer grounds the coil of the fuel pump relay for one second to do this and then will do it again for each PIP pulse it sees. If you are not cranking the engine the Computer will not see any PIP pulses.
This is done for fire safety if you hit something and the engine dies. The fuel pump will stop one second after the engine dies with the key on.
The PIP pulses come from the distributor as it turns and go to the Computer and the ICM.
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tom yuenkel
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Dec 14, 2005 09:43 PM
